2.1.2 Components of a fuel cell system

All fuel cells work broadly on the same principle:

• hydrogen or a hydrogen-rich fuel is fed to the anode, where a catalyst separates hydrogen’s negatively charged electrons from positively charged ions (protons).
• At the cathode, oxygen combines with electrons, and in some cases with species such as protons or water, resulting in water or hydroxide ions respectively.
• For polymer electrolyte membrane and phosphoric acid fuel cells, protons move through the electrolyte to the cathode to combine with oxygen and electrons to generate water.
• The electrons from the anode side of the cell cannot pass through the membrane to the positively charged cathode so they must travel around it via an electric circuit to reach the other side of the cell. This movement of electrons is an electric current.  

The design of fuel cell systems can vary significantly depending on the fuel cell type and application. However most fuel cell systems consist of four basic components:

1. A set or stack of individual cells consisting of an electrolyte sandwiched between two thin electrodes.
2. A fuel cell processor/reformer that converts the hydrogen-rich fuel into a form usable by the fuel cell, an electrolyser or a hydrogen storage system (tank or transportable cylinders). Most fuel cell systems use pure hydrogen or hydrogen-rich fuels, such as methanol, gasoline, methane, diesel or gasified coal, to produce electricity. These fuels are passed through onboard internal reformers within the fuel cell itself, or though external reformers that extract the hydrogen from the fuel.
3. Power-conditioning equipment that converts the direct current produced by the fuel cell into alternating current.
4. A number of subsystems to manage air, water, thermal energy and power.
   

Although all fuel cell power plants contain these components, the assembly of these components into the actual equipment is very important.

In addition, a heat recovery system is typically used in high-temperature fuel cell systems that are used for stationary applications where the excess energy in the form of heat can be used to produce steam or hot water or converted to electricity.